Polymeric materials have one important deficiency which must be overcome before they can be used in various commercial applications. This deficiency is the susceptibility to oxidative and actinic degradation. Many varieties of compounds have been known to be useful as stabilizers of various polymers, but all of them have certain deficiencies which limits the usefulness of such stabilizers. Thus, one class of stabilizers disclosed in the prior art that is related to the compounds of this invention is hindered hydroxybenzoates disclosed in U.S. Pat. Nos. 3,029,276; 3,112,338; 3,206,431 and 3,502,613.
Most of the compounds disclosed in said patents are various esters of 3,5-dialkyl-4-hydroxybenzoic acids while the benzoyloxybenzoates of this invention are esters of 4-(3,5-dialkyl-4-hydroxybenzoyloxy) mono (and dialkyl) benzoic acids. The most closely related compound in the prior art is ethyl-4-(3,5-di-t-butyl-4-hydroxybenzoyloxy) benzoate disclosed in U.S. Pat. No. 3,206,431. In this compound the phenyl ring in the benzoate group is completely unsubstituted while the corresponding group in the compounds of this invention has one or two alkyl substituents. Furthermore, in the prior art compound the ester group is an alkyl group while in the instant compounds the ester group is an alkylene group or oxyalkylene group having two to four benzoate moieties bonded thereto. The important difference in the properties between the prior art compounds discussed above and the benzoyloxybenzoates of this invention is the improved thermal stability of the instant compounds. This is a very important feature because the polymer substrates which are stabilized with such compounds are subjected to high temperature processing during the various manufacturing stages. Compounds which are not thermally stable will decompose during processing which will result in decreased stabilization effectiveness during the life of the polymer and also may introduce discoloration.
Furthermore, the compounds of this invention have better gas fading properties and have better water and organic solvent extraction resistance than the prior art compounds.